Semiconductor device

ABSTRACT

A lower electrode, an upper electrode provided above the lower electrode, a semiconductor chip provided between the lower electrode and the upper electrode, a pressure pad provided between the lower electrode and the upper electrode to be overlapped with the semiconductor chip, and a spiral conductor provided between the lower electrode and the upper electrode to be overlapped with the semiconductor chip and the pressure pad are provided. The spiral conductor has an upper spiral conductor, and a lower spiral conductor which is in contact with a lower end of the upper spiral conductor and faces the upper spiral conductor, and by forming grooves in the upper spiral conductor and the lower spiral conductor, a direction of a current flowing through the upper spiral conductor coincides with a direction of a current flowing through the lower spiral conductor in plan view.

FIELD

The present invention relates to a semiconductor device used, forexample, for switching large current or the like.

BACKGROUND

PTL 1 discloses a press-pack power semiconductor module. PTL 1discloses, in FIG. 1, a press-pack power semiconductor module having aplurality of semiconductor devices inside. One semiconductor device hasone semiconductor chip. The semiconductor chip is, for example, an IGBT.Electric connection in the semiconductor chip is realized by presscontact of the upper surfaces and the lower surfaces of individualelements of the semiconductor device. In order to evenly exert pressureon the plurality of semiconductor chips, a spring structure and play inan electric conduction path are needed for each semiconductor chip.

A pressure pad affords this play and secures the electric connection. Aplurality of pressure pads are occasionally provided in order toincrease current-carrying capacity for normal current. A spring isoccasionally provided between the pressure pads, it functions asinductance even when it has conductivity, and it has high impedanceparticularly for high frequency waves.

Therefore, current does not flow through the spring.

PRIOR ART Patent Literature Patent Literature 1: JP 2004-528724 ASUMMARY Technical Problem

When the semiconductor chip is in the short circuit state, currents inthe opposite directions flow through an upper electrode which is anupper bus bar and a lower electrode which is a lower bus bar.Electromagnetic force due to these currents causes repulsive force toarise between the upper electrode and the lower electrode. When therepulsive force causes the distance between the upper electrode and thelower electrode to become larger, peeling-off of a component between theupper electrode and the lower electrode occasionally occurs, so that theelectric path therebetween breaks. In particular, there is a risk ofpeeling-off on the surface of the semiconductor chip with weakconnection performance.

Further, it is considered that an electric are is generated at the siteof the electric path breaking and the device is heated due to the arc,and thereby, that an atmosphere therein expands or a solid therein isvaporized to cause its explosion. Therefore, a module needs a robustexplosion-proof structure, which has been a factor of prohibitingdownsizing thereof and low costs thereof. There are also occasionallyneeded restriction of a region of service current and/or separatelyproviding a short-circuit protection.

The present invention is devised in order to solve the aforementionedproblems, and an object thereof is to provide a semiconductor devicecapable of reducing repulsive force exerted on an upper electrode and alower electrode to prevent peeling-off of a component between the upperelectrode and the lower electrode.

Means for Solving the Problems

According to a present invention, a semiconductor device includes alower electrode, an upper electrode provided above the lower electrode,a semiconductor chip provided between the lower electrode and the upperelectrode, a pressure pad provided between the lower electrode and theupper electrode to be overlapped with the semiconductor chip, and aspiral conductor provided between the lower electrode and the upperelectrode to be overlapped with the semiconductor chip and the pressurepad, wherein the spiral conductor has an upper spiral conductor, and alower spiral conductor which is in contact with a lower end of the upperspiral conductor and faces the upper spiral conductor, and by forminggrooves in the upper spiral conductor and the lower spiral conductor, adirection of a current flowing through the upper spiral conductorcoincides with a direction of a current flowing through the lower spiralconductor in plan view.

Other features of the invention will appear more fully from thefollowing description.

Advantageous Effects of Invention

According to the present invention, since attractive force generated inthe spiral conductor reduces repulsive force exerted on the lowerelectrode and the upper electrode, peeling-off of a component betweenthe upper electrode and the lower electrode can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device according toEmbodiment 1.

FIG. 2 is a diagram illustrating the lower spiral conductor and theupper spiral conductor.

FIG. 3 is a cross-sectional view of the spiral conductor.

FIG. 4 is a partial cross-sectional view of the lower spiral conductorand the upper spiral conductor.

FIG. 5 is diagram schematically illustrating flows of currents in thespiral conductor.

FIG. 6 is a diagram exemplarily illustrating assembly of thesemiconductor devices according to Embodiment 1.

FIG. 7 is a cross-sectional view of a spiral conductor of asemiconductor device according to Embodiment 2.

FIG. 8 is a diagram illustrating a lower spiral conductor and an upperspiral conductor of a semiconductor device according to Embodiment 3.

FIG. 9 is a cross-sectional view of a semiconductor device according toEmbodiment 4.

DESCRIPTION OF EMBODIMENTS

Semiconductor devices according to embodiments of the present inventionare described with reference to the drawings. The same or correspondingcomponents are given the same signs and their duplicate description isoccasionally omitted.

Embodiment 1

FIG. 1 is a cross-sectional view of a semiconductor device according toEmbodiment 1. This semiconductor device 1 includes a lower electrode 10.A semiconductor chip 12 is provided on the lower electrode 10. Thesemiconductor chip 12 is, for example, an IGBT or a diode. A spiralconductor 20 is provided on the semiconductor chip 12. The spiralconductor 20 has a lower spiral conductor 22 and an upper spiralconductor 24.

Plates 30 and 32 formed of metal are provided to be overlapped on thespiral conductor 20. Pressure pads 34 and 36 provided on the plate 32.The semiconductor device 1 has the pressure pads 34 and 36, and thereby,they constitute a spring electrode of a press-pack power semiconductordevice. A plate 38 is provided on the pressure pads 34 and 36, and anupper electrode 40 is provided on the plate 38.

The upper ends of the pressure pads 34 and 36 are fixed to the plate 38,and the lower ends thereof are fixed to the plate 32. The pressure pads34 and 36 can expand and contract in the y-direction, that is, in thedirection perpendicular to the lower surface of the lower electrode 10and the upper surface of the upper electrode 40. Therefore, the pressurepads 34 and 36 electrically connect the lower electrode 10 and the upperelectrode 40 together via the semiconductor chip 12 regardless of thedistance between the lower electrode 10 and the upper electrode 40.

Springs 37 are provided between the pressure pads 34 and 36. The springs37 exert force which decreases the distance between the lower electrode10 and the upper electrode 40 when the distance between the lowerelectrode 10 and the upper electrode 40 increases, and exerts forcewhich increases the distance between the lower electrode 10 and theupper electrode 40 when the distance between the lower electrode 10 andthe upper electrode 40 decreases.

The individual elements between the lower electrode 10 and the upperelectrode 40 are preferably brought into press contact with one another.Thereby, electric connection between the upper electrode 40 and thelower electrode 10 can be secured via the semiconductor chip 12, thepressure pads 34 and 36, and the like.

FIG. 2 is a diagram illustrating the lower spiral conductor 22 and theupper spiral conductor 24. The top left view is a plan view of the lowerspiral conductor 22, and the cross-sectional view taken along the brokenline in this view is the bottom left view. The top right view is a planview of the upper spiral conductor 24, and the cross-sectional viewtaken along the broken line in this view is the bottom right view. Thelower spiral conductor 22 and the upper spiral conductor 24 have thesame shapes. Namely, by the lower spiral conductor 22 reversed upsidedown, it has the same shape as that of the upper spiral conductor.

Arrows in FIG. 2 indicate flows of currents. In the lower spiralconductor 22, basically, currents flow inward from the outside of thelower spiral conductor 22. Further, curved grooves 22 a are formed inthe lower spiral conductor 22. The plurality of grooves 22 a are annularas a whole. These grooves 22 a establish the flows of the currents. As aresult, in the lower spiral conductor 22, the currents flow in thecounterclockwise direction in plan view.

Meanwhile, in the upper spiral conductor 24, basically, currents flowoutward from the inside of the upper spiral conductor 24. Further,curved grooves 24 a are formed in the upper spiral conductor 24. Theplurality of grooves 24 a are annular as a whole. These grooves 24 aestablish the flows of the currents. As a result, in the upper spiralconductor 24, the currents flow in the counterclockwise direction inplan view.

As above, by forming the grooves 22 a and 24 a in the lower spiralconductor 22 and the upper spiral conductor 24, the direction of thecurrents flowing through the upper spiral conductor 24 coincides withthe direction of the currents flowing through the lower spiral conductor22 in plan view.

As apparent from the two lower views in FIG. 2, both the lower spiralconductor 22 and the upper spiral conductor 24 have conical shapes inwhich the center part rises. The lower spiral conductor 22 is convexdownward, and the upper spiral conductor 24 is convex upward. An opening22 b at the center of the lower spiral conductor 22 is provided in orderthat the lower spiral conductor 22 can easily come into contact with thesemiconductor chip 2. An opening 24 b at the center of the upper spiralconductor 24 is provided in order that the upper spiral conductor 24 caneasily come into contact with the plate 30.

FIG. 3 is a cross-sectional view of the spiral conductor 20. The upperspiral conductor 24 and the lower spiral conductor 22 are provided toface each other. The lower end of the upper spiral conductor 24 is incontact with the upper end of the lower spiral conductor 22, andthereby, they constitute the spiral conductor 20. As apparent from FIG.3, a portion of the upper spiral conductor 24 that has the largest widthis in contact with a portion of the lower spiral conductor 22 that hasthe largest width. Further, in cross-sectional view of those, thecurrents flow from a center 24A of the upper spiral conductor 24 to anoutside 24B thereof, the currents flow from an outside 22B of the lowerspiral conductor 22 to a center 22A thereof, and the currents flow tothe semiconductor chip 12.

FIG. 4 is a partial cross-sectional view of the lower spiral conductor22 and the upper spiral conductor 24. Since as mentioned above, thedirection of the currents flowing through the lower spiral conductor 22coincides with the direction of the currents flowing through the upperspiral conductor 24, attractive force arises between the lower spiralconductor 22 and the upper spiral conductor 24. FIG. 5 is a diagramschematically illustrating flows of currents in the lower spiralconductor 22 and the upper spiral conductor 24. By counterclockwisecurrents arising in the lower spiral conductor 22 and the upper spiralconductor 24, attractive force arises between these.

FIG. 6 is a diagram exemplarily illustrating assembly of thesemiconductor devices 1 according to Embodiment 1. Three semiconductordevices 1 share one lower electrode 10. Six semiconductor devices 1 arearranged on a base plate 39. FIG. 6 illustrates stacking two structuresin each of which six semiconductor devices 1 are mounted on the baseplate 39. Thereby, a press-pack power semiconductor module having twelvesemiconductor devices 1 is configured. Force is exerted on this modulefrom the top and the bottom of the module and the individual elements inthe semiconductor devices are brought into press contact with oneanother, and thereby, electric connections in the semiconductor chipsare realized.

In order to evenly exert pressure on the plurality of semiconductorchips 12, there are needed a spring structure and play in an electricconduction path for each semiconductor device 1. The pressure pads 34and 36 afford this play and secure the electric connection. While inEmbodiment 1, the two pressure pads 34 and 36 are provided in onesemiconductor device, three or more pressure pads for one semiconductordevice may be provided in order to increase the current-carryingcapacity for normal current. Notably, since the springs 37 between thepressure pads 34 and 36 function as inductance even when they haveconductivity, they have high impedance particularly for high frequencywaves, and current does not flow through the springs 37.

Now, solid arrows in FIG. 1 indicate directions of short circuitcurrents. Short circuit currents in the opposite directions flow throughthe upper electrode 40 which is an upper bus bar and the lower electrode10 which is a lower bus bar. These short circuit currents causerepulsive force to arise between the upper electrode 40 and the lowerelectrode 10. Broken arrows indicate the repulsive force. Further, sincein the semiconductor device 1 according to Embodiment 1 of the presentinvention, the attractive force arises between the lower spiralconductor 22 and the upper spiral conductor 24 as mentioned above, theattractive force cancels or reduces the repulsive force arising betweenthe upper electrode 40 and the lower electrode 10.

As above, by reducing the repulsive force exerted on the upper electrode40 and the lower electrode 10, peeling-off of a component between theupper electrode 40 and the lower electrode 10 can be prevented. Forexample, the semiconductor chip 12 can be prevented from peeling offfrom the lower electrode 10. Such prevention of peeling-off does notcause thermal expansion of an atmosphere due to an electric are, andhence, the semiconductor device and the module including the same arenot to explode. Therefore, an explosion-proof measure conventionallyprovided can be removed, which can realize downsizing and low costs ofthe module.

In the semiconductor device according to Embodiment 1 of the presentinvention, the semiconductor chip 12, the pressure pads 34 and 36provided to be overlapped with the semiconductor chip 12, and the spiralconductor 20 provided to be overlapped with the semiconductor chip 12and the pressure pads 34 and 36 are provided between the lower electrode10 and the upper electrode 40, and attractive force is generated in thespiral conductor 20. Various modifications of the semiconductor device 1according to Embodiment 1 of the present invention may occur as long asthey do not lose its features.

For example, the stacking order of the semiconductor chip 12, thepressure pads 34 and 36 and the spiral conductor 20 may be changed.Therefore, the semiconductor chip 12 can be provided above the pressurepads 34 and 36. Moreover, the number of pressure pads provided in onesemiconductor device 1 is not specially limited. As the semiconductorchip 12, a vertical chip in which current flows between its frontsurface and rear surface can be used, and such a chip is not limited toan IGBT or a diode.

While the semiconductor chip 12 may be formed of silicon, it may beformed of a wide bandgap semiconductor larger in bandgap than silicon.Examples of the wide bandgap semiconductor include silicon carbide, agallium nitride-based material, and diamond. By using the wide bandgapsemiconductor, the operable temperature of the device increases.Furthermore, silicon carbide allows a MOSFET, which is a monopolardevice, to have a high withstand voltage, which can achieve a highfrequency and high efficiency.

These modifications can also apply to semiconductor devices according tothe following embodiments. Notably, since the semiconductor devicesaccording to the following embodiments have much resemblance to that ofEmbodiment 1, their differences from that of Embodiment 1 will be mainlydescribed.

Embodiment 2

FIG. 7 is a cross-sectional view of a spiral conductor of asemiconductor device according to Embodiment 2. A portion of the upperspiral conductor 24 that has the smallest width is in contact with aportion of the lower spiral conductor 22 that has the smallest width.Namely, the center of the lower spiral conductor 22 is in contact withthe center of the upper spiral conductor 24. In this case, currententers the outside of the upper spiral conductor 24 from the outside ofthe plate 30, reaches the center of the upper spiral conductor 24, flowsoutward from the center of the lower spiral conductor 22, and enters thesemiconductor chip 12.

In plan view, clockwise currents are to arise in the upper spiralconductor 24 and the lower spiral conductor 22. In other words, since inplan view, the direction of currents flowing through the upper spiralconductor 24 coincides with the direction of currents flowing throughthe lower spiral conductor 22, attractive force arises between the upperspiral conductor 24 and the lower spiral conductor 22. Since thisattractive force reduces the repulsive force exerted on the upperelectrode 40 and the lower electrode 10, peeling-off of a componentbetween the upper electrode 40 and the lower electrode 10 can beprevented.

Embodiment 3

FIG. 8 is a diagram illustrating a lower spiral conductor 41 and anupper spiral conductor 42 of a semiconductor device according toEmbodiment 3. The top left view is a plan view of the lower spiralconductor 41, and the cross-sectional view taken along the broken linein this view is the bottom left view. The top right view is a plan viewof the upper spiral conductor 42, and the cross-sectional view takenalong the broken line in this view is the bottom right view. The lowerspiral conductor 41 and the upper spiral conductor 42 have the sameshapes. Namely, by the lower spiral conductor 41 reversed upside down,it has the same shape as that of the upper spiral conductor 42. Theupper end of the lower spiral conductor 41 is connected to the lower endof the upper spiral conductor 42, and thereby, they constitute a spiralconductor.

Both grooves 41 a of the lower spiral conductor 41 and grooves 42 a ofthe upper spiral conductor 42 are formed to be linear. In this case, byonly cutting grooves through a disc which is followed by deformation ofthe disc into a convex shape, each of the lower spiral conductor 41 andthe upper spiral conductor 42 can be simply formed.

By a current path limited by the grooves 40 a, currents flowcounterclockwise through the lower spiral conductor 41. By a currentpath limited by the grooves 42 a, currents flow counterclockwise throughthe upper spiral conductor 42. Therefore, attractive force arisesbetween the upper spiral conductor 42 and the lower spiral conductor 41.Since this attractive force reduces the repulsive force exerted on theupper electrode 40 and the lower electrode 10, peeling-off of acomponent between the upper electrode 40 and the lower electrode 10 canbe prevented.

Embodiment 4

FIG. 9 is a cross-sectional view of a semiconductor device according toEmbodiment 4. A spiral conductor 50 is provided between thesemiconductor chip 12 and the lower electrode 10. The spiral conductor50 includes a lower spiral conductor 52 provided on the lower electrode10, and an upper spiral conductor 54 provided on the lower spiralconductor 52. The structure of the spiral conductor 50 is the same asthe structure of the spiral conductor 20.

In the semiconductor device of Embodiment 4, a plurality of spiralconductors are provided to be overlapped between the lower electrode 10and the upper electrode 40. The spiral conductor 20 and the spiralconductor 50 may be directly overlapped with each other, or may beoverlapped via the semiconductor chip 12 or a plate. Since providing theplurality of spiral conductors can generate attractive forces at aplurality of places in the semiconductor device, the repulsive forceexerted on the lower electrode 10 and the upper electrode 40 can bereduced.

While in Embodiment 4 of the present invention, the two spiralconductors 20 and 50 are provided, three or more spiral conductors maybe provided in one semiconductor device. Types of the plurality ofspiral conductors are not needed to be matched into the same type. Forexample, the spiral conductor in FIG. 7 may be overlapped with thespiral conductor 20 in FIG. 1.

In Embodiments 1 to 4 above, the directions of flows of currents aredefined by forming grooves in the lower spiral conductor and the upperspiral conductor. The number and the shape of the grooves are notspecially limited as long as those guide the currents clockwise orcounterclockwise in plan view. Notably, the technical features describedfor the individual embodiments above can be properly combined.

DESCRIPTION OF SYMBOLS

10 lower electrode, 12 semiconductor chip, 20 spiral conductor, 22 lowerspiral conductor, 24 upper spiral conductor, 34,36 pressure pad, 40upper electrode

1. A semiconductor device comprising: a lower electrode; an upperelectrode provided above the lower electrode; a semiconductor chipprovided between the lower electrode and the upper electrode; a pressurepad provided between the lower electrode and the upper electrode to beoverlapped with the semiconductor chip; and a spiral conductor providedbetween the lower electrode and the upper electrode to be overlappedwith the semiconductor chip and the pressure pad, wherein the spiralconductor has an upper spiral conductor, and a lower spiral conductorwhich is in contact with a lower end of the upper spiral conductor andfaces the upper spiral conductor, and by forming grooves in the upperspiral conductor and the lower spiral conductor, a direction of acurrent flowing through the upper spiral conductor coincides with adirection of a current flowing through the lower spiral conductor inplan view.
 2. The semiconductor device according to claim 1, wherein aportion of the upper spiral conductor that has a largest width isbrought into contact with a portion of the lower spiral conductor thathas a largest width.
 3. The semiconductor device according to claim 1,wherein the grooves are formed to be curved.
 4. The semiconductor deviceaccording to claim 1, wherein a portion of the upper spiral conductorthat has a smallest width is brought into contact with a portion of thelower spiral conductor that has a smallest width.
 5. The semiconductordevice according to claim 1, wherein the grooves are formed to belinear.
 6. The semiconductor device according to claim 1, wherein aplurality of the spiral conductors are provided to be overlapped betweenthe lower electrode and the upper electrode.
 7. The semiconductor deviceaccording to claim 1, wherein the semiconductor chip is formed of a widebandgap semiconductor.
 8. The semiconductor device according to claim 7,wherein the wide bandgap semiconductor is silicon carbide, a galliumnitride-based material, or diamond.
 9. The semiconductor deviceaccording to claim 2, wherein the grooves are formed to be curved. 10.The semiconductor device according to claim 2, wherein the grooves areformed to be linear.
 11. The semiconductor device according to claim 4,wherein the grooves are formed to be linear.
 12. The semiconductordevice according to claim 2, wherein a plurality of the spiralconductors are provided to be overlapped between the lower electrode andthe upper electrode.
 13. The semiconductor device according to claim 3,wherein a plurality of the spiral conductors are provided to beoverlapped between the lower electrode and the upper electrode.
 14. Thesemiconductor device according to claim 4, wherein a plurality of thespiral conductors are provided to be overlapped between the lowerelectrode and the upper electrode.
 15. The semiconductor deviceaccording to claim 5, wherein a plurality of the spiral conductors areprovided to be overlapped between the lower electrode and the upperelectrode.